In order to eliminate a shutdown after-image, an existing thin film transistor liquid crystal display (TFT-LCD) has a function of turning on all TFTs at the moment of shutdown, i.e., an Xon function of turning on the TFTs in all rows when the TFT-LCD is shut down.
When the Xon function is enabled, an Xon signal will be decreased from a high level to a low level when it is detected that the liquid crystal display is shut down, and as shown in FIG. 1, all gate lines are turned on by a gate driving unit simultaneously. At this time, the higher a threshold voltage applied to the gate line, the more the charges on the gate line in each row and the more the current flowing through a signal line. In a process of arranging the gate driving unit on a TFT-LCD panel in a press-fit manner by using an anisotropic conductive film (ACF), after the gate driving unit is electrically coupled to the signal line of the TFT-LCD panel, some of Au particles (which serve as conductors) in the ACF are in a well-contact state while some are in a poor-contact state. In the case of few Au particles, the large current will pass through the Au particles in the well-contact state. When the TFT-LCD is shut down, if the instantaneous current on a gate signal line is too large, the current on the Au particles in the well-contact state will be large too. When the current exceeds the tolerance of the Au particles, some of the Au particles will be melted, and the instantaneous current will be withstood by the other Au particles. Upon repeated startup and shutdown, finally all the Au particles will be melted. As a result, TFTs cannot be turned on, and images will be displayed incorrectly.
In the prior art, the Xon function is usually achieved by a multi-level gate voltage (MLG) generated in a power IC. The MLG, which is used to apply a voltage to switch on a pixel TFT during the normal operation of the liquid crystal panel, is high and can lose its power rapidly (at a millisecond level) when the TFT-LCD is shut down. Within a short period of time, when the Xon function is enabled, it is difficult to ensure an appropriate value of the MLG. If the MLG is too high, the current passing through MLG lines in a peripheral gate-driving line (PLG) will be very large (larger than 200 mA) when all the gate lines are turned on. As a result, the Au particles on connection pins between a printed circuit board assembly (PCBA) and an X-chip on film (X-COF), between the X-COF and the panel, and between the panel and a Y-chip on film (Y-COF) will be burnt down easily. If the MLG is decreased too much (e.g., to 0V), the voltage for turning on the TFT will be too low when all the gate lines are turned on, and the charges on the pixels of the liquid crystal panel will not be aligned with each other rapidly. As a result, a shutdown after-image will occur.